Device for attaching turbine blades to a rotor

ABSTRACT

An annular array of circumferentially spaced rotatable turbine blades is securely fastened to a rotor by a plurality of pins having an hourglass shaped cross section; the pins fit into a plurality of axially disposed, registering grooves in the blades and rotor and provide multiple blade roots and reduce the probability of a blade flying off the rotor as fatigue cracks must initiate and propagate through a plurality of the roots to have such a failure.

1 States Patent 1 1 Saunders [451 July 17, 1973 1 DEVICE FOR ATTACHING TURBINE BLADES TO A ROTOR [75] Inventor: Paul D. Saunders, Mountain View,

21 Appl. N01: 186,611

[52] Uls- Cl 416/204, 416/220, 416/244 [51] 1M. (:1. F01d 5/32 [58] Field Of Search 416/219-221, 244, 204, 213

[56] 7 References Cited I UNITED STATES PATENTS 1,423,466 7/1922 Snyder 416/191 UX 1,831,104 11/1931 Eriksson 8! 8.1. 416/219 2,430,185 11/1947 Prescott 416/220 Perry 416/220 Jenson 416/221 FOREIGN PATENTS OR APPLICATIONS 798,613 7/1958 Great Britain 1. 416/221 Primary Examiner-Everette A. Powell, Jr. Attorney- A. T. Stratton, Fred BaehrJr. et al.

[5 7] ABSTRACT An annular array of circumferentially spaced rotatable turbine blades is securely fastened to a rotor by a plurality of pins having an hourglass shaped cross section; the pins fit into a plurality of axially disposed, registering grooves in the blades and rotor and provide multiple blade roots and reduce the probability of a blade flying off the rotor as fatigue cracks must initiate and propagate through a plurality of the roots to have such a failure.

5 Claims, 5 Drawing Figures sum 2 or 2 DEVIUE lFOIt ATTACHING TURBINE BLADES TO A ROTOR BACKGROUND OF THE INVENTION This invention relates to steam turbines and more particularly to a structure utilized for fastening the blades to the rotor.

In multi-stage turbines the number of blades in the stages varies so that it is expensive to machine the roots for each stage separately. Having a single root portion for securing each blade to the rotor also increases the probability of root failure as a flaw at the surface or close to the surface will produce stress concentration, which may result in fatigue cracks, which rapidly propagate across the entire root structure and allow the blade to fly off the rotor. Such a failure results in extensive damage to the turbine and may injure operating personnel. Thus, the desirability of a root structure which increases the remoteness of such a failure is apparent.

SUMMARY OF THE INVENTION In general, an elastic fluid machine having a rotor and an annular array of circumferentially spaced blades disposed on said rotor, when made in accordance with this invention, comprises a plurality of pins disposed axially with respect to said rotor and having a cross section shaped to securely fasten the blades to the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of this invention will become more apparent from reading the following detailed description in connection with the accompanying drawings, in which:

FIG. I is a partial perspective view of an annular array of circumferentially spaced, rotatable blades fastened to a rotor in accordance with the teachings of this invention;

FIG. 2 is a partial perspective view similar to FIG. 1 showing a modification;

FIG. 3 is a partial perspective view similar to FIG. 1 showing another embodiment of this invention;

FIG. 4 is a partial perspective view similar to FIG. 1 showing a different embodiment; and

FIG. 5 is a partial sectional view taken on line V-V of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings in detail, FIG. 1 shows a portion of an annular array of circumferentially spaced rotatable blades I disposed on a rotor 3 of a steam turbine or other elastic fluid machine. The blades I have a base portion 5, which forms segments of a ring which tightly encircles the rotor 3. The base portions 5 have a plurality of axially extending grooves 7, which register with axially extending grooves 9 in the rotor. The grooves 7 and 9 widen as they extend radially into the blades and rotor, and are properly shaped to receive a plurality of pins 11 having a cross section in the shape of an hourglass or a pair of radially disposed symmetrical lobes. The grooves 7 and 9 and pins 11 are generally rounded and have no abrupt changes in direction so that as the mating surfaces thereof engage there are no stress concentrations normally associated with rapid changes in direction of a stressed member. The rounded grooves also advantageously provide a plurality of terminating surfaces for fatigue cracks, which may develop in the base portion of the blade or in the rotor. Providing a plurality of grooves in each base portion or in the rotor allows a fatigue crack to develop and progress across a segment of the base portion of the blade or the rotor without the blade flying off the rotor as the grooves 7 and 9 act as holes drilled at the end of the crack to stop its progress through the remainder of the structure.

As shown in FIG. 2 a plurality of short pins II can be utilized to provide even greater protection against a blade flying off the rotor; since each short pin 11 is distinct, a fatigue crack initiated in one pin will not progress to adjacent pins and several pins must develop fatigue cracks and fail before a blade will fly off the rotor.

FIG. 3 shows an arrangement, wherein the base portions 5 of the blades 1 have abutting sides 13, which cooperate to form a groove 7, which registers with the groove 9 in the rotor to receive the pins 11. The grooves 7 along the edges I3 of the base portion 5 are inexpensive to manufacture and. provide additional flexibility to the overall turbine design by allowing the same number of grooves in the rotor to be utilized with a different number of blades.

In FIGS. d and 5 abutting surfaces 13' of the base portion 5' are arcuate shaped and generally conform to the shape of the cupped blade and thus extend over a greater number of pins 11 providing a more uniform distribution of stresses by supporting the blade from its leading to its trailing edge.

The fastening arrangements hereinbefore described advantageously supply a root portion with a large moment of inertia and section modulus to support vibration stresses; provide a stiff base increasing the speed at which the blade becomes resident; allow the grooves to be a standard size, reducing the machine cost; and permit the use of high strength material for forming the pins II. Utilizing high strength pins 11 reduces the size of the grooves and the amount of material, which must be machined away to form the grooves. Providing a plurality of pins maintains a high section modulus. The

dispositions of the pins is such that the stress loading is generally in tension and uniform across the pin relieving the roots of bending stresses, which are characterized by high cyclic outer fabric stresses, which result in surface fatigue cracks, which when initiated, progress rapidly through the structure.

What is claimed is:

I. An elastic fluid machine comprising a rotor havng an outer peripheral surface, an annular array of blades having an arcuate-shaped root portion, the inner surface of which forms a ring tightly encircling said outer peripheral surface of said rotor, at least one axially disposed groove in each of said root portions of said blades, said rotor having a plurality of axially disposed grooves which register with the grooves in the root portions of said blades and are generally symmetrical thereto, said grooves widening as they extend radially into said blade root portions and into said rotor, and a plurality of pins having a cross section which fits securely into said grooves to fasten said blades to said rotor.

2. An elastic fluid machine as setforth in claim 1, wherein the root portion of adjacent blades abut and said abutting surfaces are arcuate shaped so that each root portion spans a portion of a plurality of axial grooves in the rotor.

3. An elastic fluid machine as set forth in claim 2, pair of registering grooves. wherein the arcuate abutting surfaces are such that 5. An elastic fluid machine asset forth in claim 2, each pin engages the root portion of two blades. wherein there are a plurality of pins disposed in each 4. An elastic fluid machine as set forth in claim 1, pair of registering grooves.

wherein there are a plurality of pins disposed in each 5 

1. An elastic fluid machine comprising a rotor havng an outer peripheral surface, an annular array of blades having an arcuateshaped root portion, the inner surface of which forms a ring tightly encircling said outer peripheral surface of said rotor, at least one axially disposed groove in each of said root portions of said blades, said rotor having a plurality of axially disposed grooves which register with the grooves in the root portions of said blades and are generally symmetrical thereto, said grooves widening as they extend radially into said blade root portions and into said rotor, and a plurality of pins having a cross section which fits securely into said grooves to fasten said blades to said rotor.
 2. An elastic fluid machine as set forth in claim 1, wherein the root portion of adjacent blades abut and said abutting surfaces are arcuate shaped so that each root portion spans a portion of a plurality of axial grooves in the rotor.
 3. An elastic fluid machine as set forth in claim 2, wherein the arcuate abutting surfaces are such that each pin engages the root portion of two blades.
 4. An elastic fluid machine as set forth in claim 1, wherein there are a plurality of pins disposed in each pair of registering grooves.
 5. An elastic fluid machine as set forth in claim 2, wherein there are a plurality of pins disposed in each pair of registering grooves. 